Rapid processing of photographic materials including the use of phosphate ions as anti-staining agents



United States Patent O 3,132,943 RAPID PROCESSING OF PHOTOGRAPH-EC MATE- RIALS llNCLUDENG THE USE OF PHOSPHATE IONS AS ANTI-STAlNlNG AGENTS Eric Thomas Smith and Guy William Willis Stevens, Harrow, England, assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Sept. 29, 196i), Ser. No. 59,196 Claims priori application Great Britain Nov. 12, 1959 Claims. (Cl. 96-61) This invention relates to photography and more particularly to a method of preventing stain in rapid-processed photographic materials.

The rapid-processing of photographic materials to form a silver image thereby without requiring a conventional fixing is known. In such processing the photographic prints are developed in the usual way and are then treated with a solution of a stabilizer compound such as ammonium thiocyanate after which the prints are dried without washing. In the process, fixing is not required and the process materially reduces the time necessary for processing the exposed emulsion. Suitable methods proposed for the rapid processing of photographic materials have been described in Broughton et =al., US. Patent 2,614,927 issued October 21, 1952, and in Brice, US. Patent 2,448,- 857 issued September 7, 1948. The stabilizing agents employed in the processes described are compounds which contain double-bonded sulfur or an SH linkage; for example, :alkali metal and ammonium thiocyanates and thiosulfates, thioureas, thioglycol-ic acid, etc. Rapidly-develice ployed will be dependent to some extent upon the amount of ferric iron contamination to be dealt with.

In rapid processing, a silver halide photographic emulsion, preferably a gelatin-silver halide emulsion, is exposed in the usual way and developed with a suitable silver halide developing solution. After development, the excess developing solution present on the surface of the print is removed by any convenient means such as squeegee, and then the print is treated with a stabilizing solution. Treatment with the stabilizing solution may be by immersion orby surface application. The purpose of the stabilizing agent in stabilizer solutions is to make the undeveloped silver halide substantially incapable of change on further light exposure. The stabilizing agent must be a compound which does not react with metallic silver to a substantial extent and which forms a light-stable, silver complex by reaction with the undeveloped silver halide oped prints which have been stabilized with alkali metal thiocyanates and ammonium thiocyanate, according to the prior art are known to be subject to the formation of a red stain in the ultimate print. The stain presumably results from traces of ferric ion in the processing system which forms a vividly red ferric ferri-thiocyanate complex. The presence of ferric iron has also tended to accelerate the rate at which the silver image is bleached photographic prints which have been rapidly developed and stabilized with thiocyanate solutions. The bleaching of the silver image by the action of ferric iron has accordingly also had the effect of decreasing the keeping life of rapidly processed photographic materials.

It is, therefore, an object of the present invention to provide a method for improving the quality of photographic prints obtained by methods of rapid processing. Another object is to provide a method of preventing stain in rapidly processed photographic materials. A further object is to provide a method for improving the stability of rapidly developed silver images. Other objects will appear hereinafter.

These objects can be accomplished by treating thiocy-anate stabilized photographic layers with a small amount of a soluble phosphoric acid compound, such as an alkali metal phosphate, an ammonium phosphate or phosphoric acid. According to the invention the ferric ferrithiocyanate complex which is vividly red in color is prevented in photographic layers where such layers are treated with a solution containing at least one of the phosphoric acid compounds. The soluble phosphates can be incorporated in the thiocyanate-containing stabilizing solution directly or they can be contained in a separate treating bath. The concentration of the soluble phosphate in the treating bath does not appear to be critical, and additions of such phosphates as di-sodium orthophosphate ('Na HPO in the range from about 5 to about 100 grams per liter of treating solution have given satisfactory results. The preferred range is that range of quantities which give from about 3 to about 70 grams of P0 radical when added to 1 liter of treating solution; for average purposes 10 to 30 grams are suitable. The quantity emin the emulsion layer. Suitable thiocyanate stabilizing agents useful in this invention and rapid processing methods and solutions using such agents are described in Broughton et .al., US. Patent 2,614,927, issued October 21, 1952. The thiocyanate-containing stabilizing solutions according to the present invention can have incorporated therein a small amount of an alkali metal thiosulfate, or ammonium thiosulfate wherein an improvement in silver image stability is obtained. It was found that the amount of thiosulfate in a thiocyanate containing stabilizing solution to improve the silver images stabilized thereby can vary widely. Suitable proportions were found to vary from about 1 percent to about 25 percent by weight of the amount of thiocyanate compound present, with preferred amounts of thiosulfate to thiocyanate in the range from about 2 percent to about 10 percent by Weight.

The water-soluble phosphate compounds which are used to treat photographic layers stabilized with thiocyanatecontaining solutions according to the invention comprise; primary alkalimetal orthophosphates, e.g., sodium dihydrogen phosphate (NaI-I PO secondary alkali-metal orthophosphates, e.g., di-sodium hydrogen phosphate (Na HPO tertiary alkali-metal orthophosphates, e.g., trisodium phosphate (Na PO potassium phosphates, ammonium phosphates, e.g., ammonium dihydrogen phosphate (NH H PO and diammonium phosphate and solutions of phosphoric acid such as metaphosphoric acid, orthophosphoric acid, and pyrophosphoric acid.

In its normal application the water-soluble phosphoric acid compounds are incorporated directly into a thiocyanate-containingstabilizing solution. A separate treating bath containing the water-soluble phosphoric acid compounds can also be employed. Where the phosphate compounds are contained in the thiocyanate-containing stabilizer solution, it is preferred to make the stabilizing bath acid to counteract alkali present in the developing solution. Alternatively, a simplified stabilizer solution can be employed which uses sodium di-hydrogen phosphate to give the necessary acidity to the bath so that other acid producing additives are not required.

The photographic emulsions used in practicing this in: vention are generally of the developing out type. Suitable also are direct-positive emulsions such as those described in Kendall and Hill, US. Patent 2,541,472 issued February 13, 1951, and in Kendall et al., US. Patent 2,669,515 issued February 16, 1954.

The invention will now be illustrated by way of specific examples.

EXAMPLE 1 The following example illustrates a manner of treating a silver halide emulsion of the type described in Kendall and Woo-d, US Patent 2,669,515. The emulsion was exposed in a conventional manner, tor example, to a nega- 55 tive by contact or projection or if the subject is printed matter on a paper base, exposure was made by means of reflex printing methods. Thereafter the exposed element was processed by surface application of the following solutions in a small processing machine.

Table 1 Developer: Grams Sodium hydroxide 22.5 Sodium sulfite (anhydrous) 80.0 Hydroquinone 36.0 Phenidone developer 2.0 Potassium bromide 0.5

Water to 1000 cc.

The developed prints were then stabilized by treatment with a stabilizer of the following composition which contained disodium hydrogen onthophosphate according to the present invention.

Water to 1000' cc.

The pH of the above solution was 4.3 approximately. It was employed as a surface application treatment for from about 1 to about 2 seconds at 68 F. room temperature. After the stabilization treatment using Table II the prints produced thereby showed no red stain on storage and were more stable to image fading when placed in a 120 F. 75 percent relative humidity storage room for seven days. The control samples which were handled in the same manner as the test samples of this example except that the di-sodium hydrogen orthophosphate was omitted from the stabilizing solution, but the pH of which had been adjusted to 4.3 using dilute sodium hydroxide showed considerable red stain after the seven days storage period and had a reflection density of 0.95 as compared to a reflection density of 1.1 for the test prints. The reflection densities are relative image densities of the respective prints :as determined using a conventional reflection densitometer.

In the practice of the invention, it was found advantageous in some instances to vary the time of treatment of the developed prints in the stabilizing-stain-preventative solution of Table II. For example, a surface application treatment for Kodak Autopositive Paper gave optimum results when the treatment was for from 1 to about 2 seconds at 68 F. whereas a photostat-type paper, the optimum results were obtained after a surface application treatment of about 3 seconds at 130 F.

EXAMPLE 2 The following example illustrates the manner of improving the quality of a rapid-processed photographic point where sodium di-hydrogen orthophosphate is used in a typical thiocyanate stabilizing solution.

An emulsion was prepared, exposed and developed as in Example 1. Thereafter the photographic element was treated with a stabilizing-stain-preventative solution of the following composition.

Table III Grams Ammonium thiocyanate 300 Potassium metab-isulfite 50 Sodium sulfite (anhydrous) 15 Sodium thiosulfate (crystalline) Sodium dihydrogen orthophosphate (NaH PO -2H O) 100 Water to make 1000 cc.

The pH of the stabilizing solution was approximately 4.5. A surface application treatment of about 2 seconds was required to stabilize the photographic print. Improved results were obtained similar to those obtained using the stabilizer-stain-preventative composition of Example 1.

It was observed that in the foregoing examples when a small amount of sodium thiosulfiate was included in the stabilizing solutions there resulted an increased stability of the photographic print to attack by bleaching of the silver image when the photographic print was stored. The optimum concentration of sodium thiosulfate (crystalline) in a stabiiizing-st-ain-prevention composition as shown in Table H and III was about 10 grams per liter of solution. It was found that optimum results were obtained where the sodium thiosulfate was added in a range from about 5 grams to about grams per liter in a stabilizer solution containing 300 grams ammonium thiocyanate.

EXAMPLE 3 Broughton et al., US. Patent, 2,614,927, was exposed and developed according to Example 1 and thereafter treated in a stabilizer solution of the following composition.

Table IV Ammonium thiocyanate gra-ms 300 Acetic acid (glacial) cc 40 Water to make 1000 cc.

- Stabilization time in the stabilizer of the above table was about 3 seconds.

A second print was exposed and processed in asimil way except that 10 grams of sodium thiosulfate (crystalline) was added to the stabilization bath of Table IV.

Both prints were moist incubated for seven days in an incubation environment of F. and 75 percent relative humidity. The results of the trial after the seven-day period showed that while both prints lost some density on incubation, the print processed in the stabilizer without sodium thiosulfate suffered the greater density loss and the image also became more warm-toned. The reflection densities after incubation were as follows: the print treated in a bath not containing sodium thiosulfate showed a re-. fleet-ion density of 0.95, whereas the test print showed a reflection density of 1.4.

It was found that similar results were obtained using other types of emulsions, such as emulsions used in Exampics 1 and 2 of this specification. I

In applying the stabilizer composition to the surface of a photographic material according to this invention, precaution should be taken to use well-hardened emulsions to prevent the emulsion from adhering to the surface of the pad. In case the emulsion is not hardened sufficiently prior to processing, this can be done with'a formaldehyde hardening bathbefore or after the development step or in any other suitable way. Suitable hardening agents for use in the invention have been described in such references as White, U.S. Patent 2,080,019 and in US. Patents 2,725,294; 2,725,295; and 2,725,305. Emulsions may be coated on paper or other opaque supports or on any of the well known transparent supports such as cellulose nitrate, cellulose acetate, polyethylene tereph-' economic advantage of rapid-processing will accordingly be more fully realized. A further advantage of the present invention is the improvement in stability to fading of silver images which is obtained according to the invention where the Water-soluble phosphoric acid compounds and sodium thiosulfate are incorporated in thiocyanate stabilizing compositions.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it be understood that variations and modifications can be efiected Within the scope and spirit of the invention as described hereinabove and as defined in the appended claims.

What is claimed is:

1. A rapid process for producing a stable visible image in a photographic silver halide emulsion layer containing a latent image comprising developing said layer in a photographic silver halide developing solution, and immediately thereafter stabilizing said layer by applying an aqueous thiocyanate solution without substantial fixation and imbibing into said layer an aqueous solution containing phosphate ion, and drying said layer without further treatment.

2. A rapid process for producing a stable visible image in a photographic silver halide emulsion layer containing a latent image comprising developing said layer in a photographic silver halide developing solution, and immediately thereafter stabilizing said layer by applying an aqueous solution containing a compound selected from the group consisting of alkali metal thiocyanates and ammonium thiocyanate Without substantial fixation, and thereafter imbibing into said layer an aqueous solution containing at least one compound selected from the group consisting of alkali metal phosphates, ammonium phosphates, and phosphoric acid, and drying said layer Without further treatment.

3. A rapid process for producing a stable visible image in a photographic silver halide emulsion layer containing a latent image comprising developing said layer in a photographic silver halide developing solution, and immediate-1y thereafter stabilizing said layer by applying an aqueous solution containing (A) a compound selected from the group consisting of alkali metal thiocyanates and ammonium thiocyanate and (B) at least one compound selected -from the group consisting of alkali metal phosphates, ammonium phosphates, and phosphoric acid Without substantial fixation, and drying said layer Without further treatment.

4. A rapid process according to claim 3 wherein said alkali metal phosphate is disodium hydrogen phosphate.

5. A rapid process according to claim 3 wherein said alkali metal phosphate is sodium dihydrogen phosphate.

6. A rapid process according to claim 3 wherein said alkali metal phosphate is trisodium phosphate.

7. A rapid process according to claim 3 wherein said ammonium phosphate is ammonium dihydrogen phosv phate.

8. A rapid process according to claim 3 wherein said ammonium phosphate is diammonium hydrogen phosphate.

9. A rapid process according to claim 3 wherein said aqueous solution contains phosphoric acid.

I 10. A rapid process according to claim 1 wherein said aqueous thiocyanate solution'contains a mixture of ammonium thiocyanate and sodium thiosulfate.

References Cited in the file of this patent UNITED STATES PATENTS QFOREIGN PATENTS Great Britain Sept. 23, 1949 OTHER REFERENCES Crabtree: Rapid Processing of Films and Papers, P.S.A. Journal, February 1949, vol. 15, pp. -135, 

1. A RAPID PROCESS FOR PRODUCING A STABLE VISIBLE IMAGE IN A PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER CONTAINING A LATENT IMAGE COMPRISING DEVELOPING SAID LAYER IN A PHOTOGRAPHIC SILVER HALIDE DEVELOPING SOLUTION, AND IMMEDIATELY THEREAFTER STABILIZING SAID LAYER BY APPLYING AN AQUEOUS THIOCYANATE SOLUTION WITHOUT SUBSTANTIAL FIXATION AND IMBIBING INTO SAID LAYER AN AQUEOUS SOLUTION CONTAINING PHOSPHATE ION, AND DRYING SAID LAYER WITHOUT FURTHER TREATMENT. 